In the power supply of the high-frequency heating device (for example, a microwave oven) with a magnetron as a load, it often needs to change on-off time (a frequency or a duty ratio) of a main switching element, for example, an IGBT (Insulated Gate Bipolar Transistor), so as to regulate an output power of the power supply. A voltage control mode is adopted generally in a conventional way. That is, a circuit is controlled to output a certain pulse width according to a value of an input voltage and a required output power, such that the on-off time of the main switching element is controlled. In principle, the higher the input voltage is, the smaller the turn-on time of the IGBT is; the greater the output power is, the greater the turn-on time of the IGBT is. This control mode is more complicated and strict in a timing sequence of software, and a maximum current cannot be controlled during the whole procedure and there are high requirements for the switching element.
The waveform of the input voltage and the switch waveform of the IGBT in the related art may be shown in FIG. 1. A software adjustment may be performed on the driving of the IGBT by using a sequential control mode. The controller continuously controls the main switching element (for example, IGBT) to turn on and turn off according to a preset on-off program. The whole heating device is turned off and the operation ends if reaching a preset over-current protection voltage. The resource consumption of the controller is bigger and the over-current protection cannot be performed timely in this control mode.